1. Field of the Invention
The present invention relates to a rotation-resisting wire rope, and particularly relates to a long rotation-resisting wire rope for use in overhead cranes and the like.
2. Description of the Related Art
There are various types of construction for wire ropes (mentioned as ropes hereinafter), and the ropes are used based on standards such as Japanese Industrial Standards (JIS). Among them, the ropes under JIS No. 13 or JIS No. 18 are generally used for cranes, and are rotating wire ropes. The rotating property is a characteristic of wire rope to rotate by itself when tension is added to the wire rope. For ladle cranes at steelmaking yard, a long wire rope is run over a plurality of sheaves and sustains a heavy load. In using a rotating wire rope for such a crane, the wire rope often rotates between sheaves (pulleys) while the rope is being repeatedly run over the sheaves. The rope is repeatedly alternately bent in mutually opposite directions while being run over a plurality of sheaves, thus shortening the lifespan of the rope by fatigue, which has been considered a problem.
In order to solve this problem, there has been an attempt to use so-called non-rotating wire ropes or rotation-resisting wire ropes. The rotation-resisting property means that the rotating force of a wire rope is small when tension is added to the wire rope.
In Japanese Unexamined Patent Application Publication No. 8-92885, a rotation-resisting wire rope is proposed that has a multi-ply laid core strand having shaped wires with a flattened surface at least at an outermost ply and a plurality of core strands provided around the periphery of the core strand and laid in the same direction as the lay of the core strand. Side strands are laid in the direction opposite to the lay of the core strand so as to form a wire rope, and a pitch multiple of the rope is larger than that of the side strands.
This proposal can somewhat solve the conventional problem wherein bending directions are reversed as a wire rope is run over sheaves and the wire rope repeatedly alternately receives bending stress in mutually opposite directions while being run over a plurality of sheaves, which shortens the lifespan of the wire rope by fatigue. However, the rotation-resisting property of the above-noted technique is insignificant. There are also some remaining problems, including breakage due to contact of external wires of a wire rope against sheaves and a decrease in lifespan due to breakage by contact between core strands and side strands.
An object of the present invention is to solve the above-noted problems of conventional rotation-resisting wire ropes. More specifically, it is an object of the present invention to provide a long wire rope for, for example, overhead cranes that is practically non-rotating but is unlikely to be broken by wear and fatigue.
In order to solve the above-noted problems, the present inventors conceived and tested various constructions of wire ropes and invented the present invention.
Specifically, a rotation-resisting wire rope of the present invention has a plurality of side strands, each side strand having wires that are laid in the same direction as the lay of core strand wires, around the periphery of a core strand. The side strands are laid in the direction opposite to the lay of the core strand wires so as to form a wire rope. A pitch multiple of the wires of the side strands is preferably smaller than a pitch multiple of the wire rope. Ratios between a diameter of the side strands and a diameter of the core strand are preferably about 1.3 to about 1.8. The pitch multiple of the wires of the side strands is preferably about 5 to about 8, and the pitch multiple of the wire rope is preferably about 8 to about 10. Both the core strand and the side strands preferably have shaped wires with a flattened surface at an outermost ply.